1. Field of the Invention
The present invention relates to a circuit for restoring logic levels of bits transmitted asynchronously and serially in a signal. The present invention relates more particularly to a circuit that properly restores bits even when a transmission signal undergoes phase and amplitude variations.
2. Discussion of the Related Art
FIG. 1 shows an example of a transmission signal 9. The transmission signal 9 is used to transmit teletext information 11. Each line of teletext information begins with a synchronization burst 10.
Depending on the conditions at a receiving circuit, a teletext signal may include noise, and be of variable amplitude and phase. However, using the synchronization burst 10 at the beginning of each line of teletext information 11, the circuit receiving the transmission signal 9 can periodically readjust its receive phase and a discrimination threshold used to distinguish the high logic levels from the low logic levels in the lines of teletext information.
U.S. Pat. No. 5,136,382 describes a circuit for receiving lines of teletext information included in a transmission signal. The frequency and the discrimination threshold found at the beginning of each line are maintained for the entire duration of the line, until the next synchronization pulse burst. Thus, the circuit does not compensate for possible amplitude and phase fluctuations in a line of the teletext information, which could result in many errors if the conditions at the receiving circuit are not optimal.